Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, Sept. 2004. / Thesis Advisor(s): Peter C. Chu. Includes bibliographical references (p. 73). Also available online.

Thesis (Ph. D.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2004. / Includes bibliographical references (p. 159-166).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

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Thesis (Ph. D.)--University of California, San Diego, 1997. / Vita. Includes bibliographical references.

Miniature Autonomous Underwater Vehicles are a major area of research and development today. Because of their size and agility, they are capable of exploring and operating in smaller bodies of water in addition to areas of the ocean that would be out of reach for a larger vehicle. Being autonomous requires that the system must be capable of performing without the need for human supervision, so use of external sensors such as sonar are needed to ensure the safety of the vehicle during missions. However, since all of the onboard instrumentation and external equipment must also be miniature in size, the implementation of a small sonar system is desirable. This thesis contains a brief introduction to sound and sonar, leading into a description of the design and development of a small, inexpensive sonar altimeter. Piezoelectric material is used for transduction in the sonar system while a PIC microcontroller processes the return signals from the water. This altimeter was made to be implemented on a miniature autonomous underwater vehicle developed by the Autonomous Systems and Controls Laboratory at Virginia Polytechnic Institute. In addition to being capable of reporting ocean depths, sonar systems can be used to aid in the navigation of underwater vehicles. A constant altitude controller based on sonar data has been designed, tested, and implemented on the autonomous underwater vehicle. Possibilities for an obstacle avoidance system involving sonar are also discussed in this thesis. / Master of Science

Radar altimeters were originally designed to study ocean geodynamics, where the scattering processes are governed entirely by the surface features. These same altimeters have recorded data from over the polar ice sheets, where the scattering processes cannot in general be limited to surface properties. Radar pulse penetration, which gives rise to volume scattering, must also be accounted for in these return waveforms. This pulse penetration affects the altimeter range measurements as well as other information that is derived from the altimeter waveform data. To aid in the study of pulse penetration effects, a waveform model for combining surface and volume scattering effects in the estimation of the radar altimeter returns recorded over continental ice and snow is developed and discussed. The surface scattered waveform model is based on the well-known impulse response method which is capable of accounting for arbitrary altitude, beamwidth, pulsewidth and pointing angle. The newly formulated volume scattered waveform model is also an impulse response based method which differs from previous versions in that it can also be applied to a general altimeter configuration. The two models are time registered and then added together in an arbitrary ratio representing the relative contributions of surface and volume scattering to the overall return power waveform. The combined model can be used to study actual altimeter waveforms by varying the important parameters, including surface roughness and effective extinction coefficient. The capabilities and limitations of this new combined model are also discussed and guidelines for its use are detailed. The combined model is tested by comparing it to the Multimode Aircraft Radar Altimeter (MARA) data which were recorded over and around the Greenland ice sheet in September 1991. Evaluation of this averaged waveform data identified problems that were encountered with the MARA design. A number of techniques are developed in an effort to account for and correct these problems, but none of these attempts were completely successful. The 1991 MARA data are considered usable for waveform analysis, but with the understanding that some error may be present in the final results. The MARA data obtained from the Greenland ice sheet are analyzed for estimates of surface roughness, effective extinction coefficient and ratio of surface to volume scattering strengths. A simple optimization method is employed which achieves a least-squares fit of the combined model to the altimeter data. The result is an estimate of these parameters as a function of location on the ice shelf. To the author's knowledge, this is the first time both surface- and volume-related parameters have been estimated simultaneously from Ka-band radar data. / Ph. D.

Inom fallskärmshoppning behövs förutom ett välfungerande fallskärmssystem även en precis höjdmätare. Båda är avgörande komponenter när det gäller utrustning för att kunna genomföra ett säkert hopp. Genom digitalisering och den tekniska utvecklingen finns det idag intressen för att ta fram en digital höjdmätare med bättre precision, flera funktioner och bättre samt tydligare användargränssnitt. Det existerar ett flertal tekniker för mätning av höjd. De tekniker som tas upp i examensarbetet är global positioning system (GPS), radar och barometer. Målet med examensarbetet var att ta fram en robust algoritm för mätning av höjd, med möjlighet till utveckling. Examensarbetet skulle även innehålla riskanalys av vald(a) teknik(er) , samt förslag på lämpliga presentationstekniker och systemlösningar satt i ett större perspektiv. Systemlösningarna skulle vara anpassade för enkel integration av nya funktioner. I mån av tid skulle även en prototyp utvecklas samt testas. Metoden som valdes var en digital höjdmätare på grund av att den passade bäst för det mål som upprättats för projektet. Fr att beräkna höjden med den digitala höjdmätaren användes sambandet mellan lufttryck och höjd. Resultatet av dessa beräkningar visade på ett tillräckligt precist mätvärde för att vara godtagbart. Eftersom mätvärdets precision var godtagbar beslutades det att inga ytterligare rättningar skulle göras. Arbetet fortsattes med att utveckla en prototyp och testning av denna utfördes. Resultatet blev att en fungerande prototyp togs fram. Framtida utvecklingsmöjligheter finns inom presentationsteknik, chassi, ytterligare rättningar av formeln för höjdmätning och fler iterationer av hårdvaran. / In skydiving, in addition to a well-functioning parachute system, a good and precise altimeter is needed. Both which are crucial parts of equipment in order to be able to perform a safe jump. Through digitalization and the technological development, there are today interests of developing a digital altimeter with better precision and several functions There are a number of techniques for measuring altitude. Those that are included in this bachelor thesis are GPS, radar and barometers. The aim of the thesis was to develop a robust algorithm for measuring height, with the possibility of development. The thesis work would also include risk analysis of selected technology or techniques, as well as suggestions for suitable presentation techniques and system solutions in a larger perspective. The system solutions would be adapted for easy integration of new features. If time allowed it, a prototype would also be developed and tested. The method chosen was a digital altimeter because it was best suited for the goals set for the project. To calculate the height with the digital altimeter, the relationship between air pressure and height was used. The result of these calculations showed a sufficiently precise measurement value to be acceptable. Since the accuracy of the measurement value was acceptable, it was decided that no further corrections would be made. The work continued with developing a prototype and testing it. The result was a functioning prototype. Future development opportunities are available within presentation technology, chassis, further corrections of the formula for height measurement and more iterations of hardware.

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